II. Passage from uterine lumen to blastocyst fluid

Summary

Passage of bovine serum albumin (BSA) into unimplanted rabbit blastocysts was studied using intravenous or intrauterine injection of the mother and in vitro cultivation of 5-day blastocysts. BSA concentration in blastocyst fluid was measured using a quantitative radial immunodiffusion method and confirmed by double diffusion in agar.

Intravenous injection of up to 200 mg/kg body weight produced a mean concentration of 106 μg/ml in uterine fluid and the blastocyst fluid was mostly negative. In vitro cultivation with 1–20 mg BSA/ml resulted in appreciable passage which was confirmed by intra-uterine injection. BSA appeared in blastocyst fluid after 2–3 h of exposure. After 24 h, 0·25–2·0 μg BSA was accumulated. The highest concentration observed in blastocyst fluid was 338 μg/ml and this was about 1·7% of the surrounding concentration. Combined with previous results on passage from plasma into uterine fluid, it could be calculated that in 24 h the blastocyst fluid acquired about 0·08% of the maternal serum concentration of BSA.

The accumulation of BSA by the blastocyst is about half that of rabbit albumin in the same period (5–6 days p.c.), which suggests that the unimplanted blastocyst is capable of discriminating between native and foreign serum albumin.

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